Phase-shifting circuits are used in many applications in electronics, both in signal processing and in power electronics. In general, a circuit is designed to produce a given phase difference at a given frequency. The circuit must be modified for another phase angle or another frequency.
The circuits and methods described in the document U.S. Pat. No. 6,744,296 changed this situation since the phase-offset angle can be continuously adjusted by a voltage independently of the frequency.
However, the analogue components used partly in the above circuits do not guarantee the generation of very precise phase differences required by certain applications.
This is the case in particular in automotive applications, such as electronic ignition, or the control of brushless electrical motors/generators.
The document U.S. Pat. No. 4,788,957, for example, therefore proposes to improve the devices for controlling the ignition point of internal combustion engines by using a phase-difference circuit and an auto-ignition detector formed by a computer.
One obstacle to making fully digital methods in the field more widespread, although they are advantageous with regard to flexibility of implementation and cost compared with analogue methods, has been the great calculation power necessary for following the rapid variations in the signals.
The appearance on the market of multiprocessor microcontroller components dispenses with this constraint provided that they are programmed appropriately.
The document U.S. Pat. No. 5,317,248 discloses precisely a way of programming an MC68332 microcontroller from Motorola in order to generate control pulses, width modulated, for polyphase electrical machines.
The MC68332 microcontroller also has a central processing unit, or CPU (CPU is the English acronym for Central Processing Unit), a calculation unit dedicated to temporal events, or TPU (TPU is the English acronym for Time Processor Unit). The TPU has programmable delay circuits (known to persons skilled in the art by the English term “timer”) and programmable pulse width modulation modules, referred to as PWM modules (PWM is the English acronym for Pulse Width Modulation).
The TPU generates a synchronisation signal and pulses centered on the edges of this signal.
The algorithms described in the document U.S. Pat. No. 5,317,248 to delimit transit times and jitter but the method used seems to be applicable only in the case where the signals generated are out of phase only with respect to a single synchronisation signal, coming from a single sensor sensing the position of the rotor of the machine.
However, it is known that it is preferable for a polyphase electrical machine to comprise one position sensor for each phase in order to quickly detect variations in the speed of the rotor.